Risk / reward I guess. The risk for a copyright holder suing them is pretty low. If they sue and lose it could jeopardize everything (legitimize sharing) vs. winning a few bucks squashing a single pirate site, when 10 more will pop up the next day. Better to let it be and chalk it up to “cost of doing business”.
The court costs alone probably make it very unlikely.
I used to think sharing GPL was a little shady myself, but then I realized- HEY, they chose that license. That is the way they want it. If I need support, I will pay for support.
It would be nice if there was a donate to author button on the website. This would help encourage GPL I think. I always try and donate whenever I use something FREE to encourage the practice, especially if it is used for commercial purposes.